In general, the washing control of a washing machine is carried out by setting washing water level and washing period of time depending on the detected amount of laundry introduced into a washing tub.
FIG. 1 is a washing control system of a washing machine including a key pad 101 generating key signals to select a desired washing cycle such as number of times of washing, of rinsing, and of drying, washing course, and washing period of time to be taken according to a user's pressing of the keys, a system control part 100 controlling overall system operation of the washing machine in response to the key signals selected in the key pad 101, a motor operation part 102 having triac TA1 and TA2 controlling operation of a washing motor 103 by switching on/off applied alternative current power in response to the control signals transmitted from the system control part 100, laundry quantity sensing part 104 having resistances R11 and R12, diodes D11 and D12, and a photocoupler PC1, sensing quantity of laundry inside of a washing tub and transmitting to the system control part 100 using the residual power generated by the inertia of the washing motor 103 after turn-off of the washing motor 103, and a display part displaying various status of operations in response to the control signals of the system control part 104.
When a user, after introducing laundry into the washing tub, sets up a washing cycle by pressing washing keys on the key pad 101, the system control part 100 reads in the key signals and initiates washing operation of the washing machine. That is, a feed water valve(not shown) is opened to feed washing water up to a predetermined level.
When feeding of washing water has been completed, the system control part 100 switches on/off the triacs TA1 and TA2 of the motor operation part alternatively for a certain time to detect the quantity of laundry introduced into the washing tub. Accordingly, the washing motor 103 rotates either in clockwise or anticlockwise direction alternatively. After a certain period of time has been lapsed, the system control part 100 switches off the triacs TA1 and TA2 of the motor operation part 102 to stop driving of the motor 103. In this time, the washing motor 103 slows down by the inertia of the washing motor 103 until it comes to a complete stop.
When there is more laundry in the washing tub, the rotation of the washing motor 103 would stop earlier due to more friction between a pulsator and laundry, and, when there is less laundry, the rotation speed of the washing motor 103 would decrease slowly due to less friction.
The laundry quantity sensing part 104 detects the residual voltage generated by the inertia of the washing motor 103, carries out waveform shaping thereof and transmits therefrom to the system control part 100. In another words, the residual power generated in the washing motor 103 depending on the quantity of laundry, turns on/off a light emitting diode LD11 through the resistance R11 and the diode D11 of the laundry quantity sensing part 104. As a light receiving element TR11 is turned on/off depending on the turn on/off of the light emitting diode LD11, power source electrode voltage Vcc is transmitted to the system control part 100 through the resistance R12 in waveform.
The system control part 100 determines the quantity of laundry according to the number of waves obtained by the laundry quantity sensing part 104, based on which quantity, one of washing water levels of high, middle and low as well as washing period of time are determined.
For example, when small number of waves are transmitted from the laundry quantity sensing part 104, determining quantity of laundry being great, the washing period of time is set longer and the washing water level is set high, and when the number of waves transmitted from the laundry quantity sensing part 104 is great, determining quantity of laundry being little, the washing period of time is set shorter and the washing water level is set low.
After setting the washing water level and washing period of time as foregoing description, the system control part 100 opens to supply washing water up to the set level, and drives the washing motor 103 in pulsating manner through the motor operation part 102, carrying out washing, which is displayed on the display part 105.
However, as the settings of washing operation is determined according to the current(residual voltage), the foregoing washing machine can detect the quantity of laundry approximately, but not exactly due to the serious dependency of the current(residual voltage) on the characteristics of the washing motor, belt tension and slip on and between the washing motor and the clutch, operating voltage of the washing motor and the disposed condition of the laundry in the washing tub. Accordingly, because the washing water quantity and the washing period of time, rate of rinse, and drying period of time can not be set properly, damage of laundry, waste of power and water can be caused.
And, because the properties of the laundry in the washing tub can not be known, there is problem in forming of proper washing water current in the washing tub and subsequent performing optimum washing.